The present invention relates to a process for the production of homogeneous polyolefin rubber-oil viscous liquid mixtures containing an equal or predominant amount by weight of oil.
It has long been known to extend elastomers with oil for economical and technical reasons. One common conventional process involves adding oil to a solution or dispersion of the rubber prior to precipitation, and precipitating the oil together with the rubber in the manufacturing plant. See S. Bostroem, "Kautschuk-Handbuch" (Rubber Handbook), Berliner Union/Stuttgart, 1959, vol. 1, p. 362. This process is used only rarely, for reasons of expense and difficulties in the processing technique, in order to produce oil-extended rubbers having more than 100 parts by weight of oil per 100 parts by weight of rubber.
Another known process utilized by rubber processing companies is characterized by the production of rubber-oil batches shortly before or during the manufacturing of so-called rubber mixtures. These known mixtures contain, in addition to the rubber and/or oil, fillers, "Factice" substances, metallic oxides, fatty acids, coloring agents, vulcanizing agents, vulcanization accelerators, antiaging substances and/or stabilizers, waxes, and other recipe components known in the rubber industry. The oil is added to the rubber or rubber mixtures in these processes either with the aid of conventional mixing devices of the rubber industry, e.g., roll mills, internal mixers with and without a plunger, etc., or with more recently developed mixing units, e.g., continuously operating mixers described in S. Bostroem, "Kautschuk-Handbuch" Berliner Union/Stuttgart, 1959, vol. 1, p. 362. The preparation of rubber-oil mixtures containing more than 100 parts by weight of oil per 100 parts by weight of rubber causes technical difficulties when such a process is employed unless unusually high doses of filler are employed and special mixing conditions are maintained, e.g., the premixing of a rubber-oil batch with a particularly low viscosity to facilitate the adsorption of larger amounts of oil, or the use of especially sealed mixing units.
It is known from German Unexamined Laid-Open Application DOS 1,814,842, to extend rubber copolymers of at least two different .alpha.-olefins with up to 350 parts by weight of oil. According to this method, the rubber is allowed to stand in the oil for a period of time without substantial stirring, so that the oil can diffuse into the rubber. The production of highly oil-extended rubbers and/or of rubber-oil mixtures having a rubber:oil ratio of at least 1:1 is possible according to this process only at a high cost in time and space. For reasons of economy and available space, especially in those cases where larger amounts of elastomer are to be extended with oil, this process is unsuitable.
British Patent 962,519, the contents of which are incorporated by reference herein, describes elastomeric hydrocarbon copolymers of at least one .alpha.-monoolefin and at least one non-conjugated diene which are extended with specific petroleum oils to give normally solid, sulfur curable mixtures. The process of the present invention is not limited to the particular petroleum oils described therein and is used to prepare homogenous liquid compositions of high oil content which can be readily blended with either solid or liquid compositions.
Finally, U.S. Pat. No. 3,679,380 discloses the use of liquid ethylene-.alpha.-olefin copolymers and/or of liquid ethylene- .alpha.-olefin-diene terpolymers in the extremely low-molecular weight range (Mn &lt;18,000) to improve various properties of mineral oils. However, these extremely low-molecular weight co- and/or terpolymers of ethylene possess uncommon properties with respect to Mooney viscosity and accordingly they require a special manufacturing process for each case.
Because of the advantageous properties of elastomeric copolymers of .alpha.-olefins optionally with non-conjugated dienes, it would be highly desirable to expand the scope of possible applications by providing a technically acceptable method for preparing highly oil-extended, homogeneous copolymer compositions.
In view of the above-discussed processes of the current state of the art, there is a genuine need for a simple and economical process for the manufacture of rubber-oil mixtures, specifically of polyolefin rubber-oil mixtures, wherein the rubber to oil ratio is at least 1:1 and wherein rubbers in the usual plasticity and/or viscosity range, i.e., having a viscosity of 5 to 150 ML.sub.1.sub.+4 (100.degree.C) can be employed.